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/**
* Copyright 2013 Matija Mazi.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.bitcoinj.crypto;
import com.google.common.collect.*;
import org.bitcoinj.core.*;
import org.spongycastle.math.ec.*;
import java.math.*;
import java.nio.*;
import java.security.*;
import java.util.*;
import static com.google.common.base.Preconditions.*;
/**
* Implementation of the BIP 32
* deterministic wallet child key generation algorithm.
*/
public final class HDKeyDerivation {
static {
// Init proper random number generator, as some old Android installations have bugs that make it unsecure.
if (Utils.isAndroidRuntime())
new LinuxSecureRandom();
RAND_INT = new BigInteger(256, new SecureRandom());
}
// Some arbitrary random number. Doesn't matter what it is.
private static final BigInteger RAND_INT;
private HDKeyDerivation() { }
/**
* Child derivation may fail (although with extremely low probability); in such case it is re-attempted.
* This is the maximum number of re-attempts (to avoid an infinite loop in case of bugs etc.).
*/
public static final int MAX_CHILD_DERIVATION_ATTEMPTS = 100;
/**
* Generates a new deterministic key from the given seed, which can be any arbitrary byte array. However resist
* the temptation to use a string as the seed - any key derived from a password is likely to be weak and easily
* broken by attackers (this is not theoretical, people have had money stolen that way). This method checks
* that the given seed is at least 64 bits long.
*
* @throws HDDerivationException if generated master key is invalid (private key 0 or >= n).
* @throws IllegalArgumentException if the seed is less than 8 bytes and could be brute forced.
*/
public static DeterministicKey createMasterPrivateKey(byte[] seed) throws HDDerivationException {
checkArgument(seed.length > 8, "Seed is too short and could be brute forced");
// Calculate I = HMAC-SHA512(key="Bitcoin seed", msg=S)
byte[] i = HDUtils.hmacSha512(HDUtils.createHmacSha512Digest("Bitcoin seed".getBytes()), seed);
// Split I into two 32-byte sequences, Il and Ir.
// Use Il as master secret key, and Ir as master chain code.
checkState(i.length == 64, i.length);
byte[] il = Arrays.copyOfRange(i, 0, 32);
byte[] ir = Arrays.copyOfRange(i, 32, 64);
Arrays.fill(i, (byte)0);
DeterministicKey masterPrivKey = createMasterPrivKeyFromBytes(il, ir);
Arrays.fill(il, (byte)0);
Arrays.fill(ir, (byte)0);
// Child deterministic keys will chain up to their parents to find the keys.
masterPrivKey.setCreationTimeSeconds(Utils.currentTimeSeconds());
return masterPrivKey;
}
/**
* @throws HDDerivationException if privKeyBytes is invalid (0 or >= n).
*/
public static DeterministicKey createMasterPrivKeyFromBytes(byte[] privKeyBytes, byte[] chainCode) throws HDDerivationException {
BigInteger priv = new BigInteger(1, privKeyBytes);
assertNonZero(priv, "Generated master key is invalid.");
assertLessThanN(priv, "Generated master key is invalid.");
return new DeterministicKey(ImmutableList.of(), chainCode, priv, null);
}
public static DeterministicKey createMasterPubKeyFromBytes(byte[] pubKeyBytes, byte[] chainCode) {
return new DeterministicKey(ImmutableList.of(), chainCode, new LazyECPoint(ECKey.CURVE.getCurve(), pubKeyBytes), null, null);
}
/**
* Derives a key given the "extended" child number, ie. the 0x80000000 bit of the value that you
* pass for childNumber will determine whether to use hardened derivation or not.
* Consider whether your code would benefit from the clarity of the equivalent, but explicit, form
* of this method that takes a ChildNumber rather than an int, for example:
* deriveChildKey(parent, new ChildNumber(childNumber, true))
* where the value of the hardened bit of childNumber is zero.
*/
public static DeterministicKey deriveChildKey(DeterministicKey parent, int childNumber) {
return deriveChildKey(parent, new ChildNumber(childNumber));
}
/**
* Derives a key of the "extended" child number, ie. with the 0x80000000 bit specifying whether to use
* hardened derivation or not. If derivation fails, tries a next child.
*/
public static DeterministicKey deriveThisOrNextChildKey(DeterministicKey parent, int childNumber) {
int nAttempts = 0;
ChildNumber child = new ChildNumber(childNumber);
boolean isHardened = child.isHardened();
while (nAttempts < MAX_CHILD_DERIVATION_ATTEMPTS) {
try {
child = new ChildNumber(child.num() + nAttempts, isHardened);
return deriveChildKey(parent, child);
} catch (HDDerivationException ignore) { }
nAttempts++;
}
throw new HDDerivationException("Maximum number of child derivation attempts reached, this is probably an indication of a bug.");
}
/**
* @throws HDDerivationException if private derivation is attempted for a public-only parent key, or
* if the resulting derived key is invalid (eg. private key == 0).
*/
public static DeterministicKey deriveChildKey(DeterministicKey parent, ChildNumber childNumber) throws HDDerivationException {
if (!parent.hasPrivKey()) {
RawKeyBytes rawKey = deriveChildKeyBytesFromPublic(parent, childNumber, PublicDeriveMode.NORMAL);
return new DeterministicKey(
HDUtils.append(parent.getPath(), childNumber),
rawKey.chainCode,
new LazyECPoint(ECKey.CURVE.getCurve(), rawKey.keyBytes),
null,
parent);
} else {
RawKeyBytes rawKey = deriveChildKeyBytesFromPrivate(parent, childNumber);
return new DeterministicKey(
HDUtils.append(parent.getPath(), childNumber),
rawKey.chainCode,
new BigInteger(1, rawKey.keyBytes),
parent);
}
}
public static RawKeyBytes deriveChildKeyBytesFromPrivate(DeterministicKey parent,
ChildNumber childNumber) throws HDDerivationException {
checkArgument(parent.hasPrivKey(), "Parent key must have private key bytes for this method.");
byte[] parentPublicKey = parent.getPubKeyPoint().getEncoded(true);
assert parentPublicKey.length == 33 : parentPublicKey.length;
ByteBuffer data = ByteBuffer.allocate(37);
if (childNumber.isHardened()) {
data.put(parent.getPrivKeyBytes33());
} else {
data.put(parentPublicKey);
}
data.putInt(childNumber.i());
byte[] i = HDUtils.hmacSha512(parent.getChainCode(), data.array());
assert i.length == 64 : i.length;
byte[] il = Arrays.copyOfRange(i, 0, 32);
byte[] chainCode = Arrays.copyOfRange(i, 32, 64);
BigInteger ilInt = new BigInteger(1, il);
assertLessThanN(ilInt, "Illegal derived key: I_L >= n");
final BigInteger priv = parent.getPrivKey();
BigInteger ki = priv.add(ilInt).mod(ECKey.CURVE.getN());
assertNonZero(ki, "Illegal derived key: derived private key equals 0.");
return new RawKeyBytes(ki.toByteArray(), chainCode);
}
public enum PublicDeriveMode {
NORMAL,
WITH_INVERSION
}
public static RawKeyBytes deriveChildKeyBytesFromPublic(DeterministicKey parent, ChildNumber childNumber, PublicDeriveMode mode) throws HDDerivationException {
checkArgument(!childNumber.isHardened(), "Can't use private derivation with public keys only.");
byte[] parentPublicKey = parent.getPubKeyPoint().getEncoded(true);
assert parentPublicKey.length == 33 : parentPublicKey.length;
ByteBuffer data = ByteBuffer.allocate(37);
data.put(parentPublicKey);
data.putInt(childNumber.i());
byte[] i = HDUtils.hmacSha512(parent.getChainCode(), data.array());
assert i.length == 64 : i.length;
byte[] il = Arrays.copyOfRange(i, 0, 32);
byte[] chainCode = Arrays.copyOfRange(i, 32, 64);
BigInteger ilInt = new BigInteger(1, il);
assertLessThanN(ilInt, "Illegal derived key: I_L >= n");
final BigInteger N = ECKey.CURVE.getN();
ECPoint Ki;
switch (mode) {
case NORMAL:
Ki = ECKey.publicPointFromPrivate(ilInt).add(parent.getPubKeyPoint());
break;
case WITH_INVERSION:
// This trick comes from Gregory Maxwell. Check the homomorphic properties of our curve hold. The
// below calculations should be redundant and give the same result as NORMAL but if the precalculated
// tables have taken a bit flip will yield a different answer. This mode is used when vending a key
// to perform a last-ditch sanity check trying to catch bad RAM.
Ki = ECKey.publicPointFromPrivate(ilInt.add(RAND_INT).mod(N));
BigInteger additiveInverse = RAND_INT.negate().mod(N);
Ki = Ki.add(ECKey.publicPointFromPrivate(additiveInverse));
Ki = Ki.add(parent.getPubKeyPoint());
break;
default: throw new AssertionError();
}
assertNonInfinity(Ki, "Illegal derived key: derived public key equals infinity.");
return new RawKeyBytes(Ki.getEncoded(true), chainCode);
}
private static void assertNonZero(BigInteger integer, String errorMessage) {
if (integer.equals(BigInteger.ZERO))
throw new HDDerivationException(errorMessage);
}
private static void assertNonInfinity(ECPoint point, String errorMessage) {
if (point.equals(ECKey.CURVE.getCurve().getInfinity()))
throw new HDDerivationException(errorMessage);
}
private static void assertLessThanN(BigInteger integer, String errorMessage) {
if (integer.compareTo(ECKey.CURVE.getN()) > 0)
throw new HDDerivationException(errorMessage);
}
public static class RawKeyBytes {
public final byte[] keyBytes, chainCode;
public RawKeyBytes(byte[] keyBytes, byte[] chainCode) {
this.keyBytes = keyBytes;
this.chainCode = chainCode;
}
}
}
